In an effort to provide the health care industry with bone substitute materials for the treatment of broken or deteriorating bone, a variety of compositions have been developed. When using bone substitute materials, a physician will typically remove the broken or deteriorated portion of the natural bone and replace it with the bone substitute material.
Cement compositions that currently find use in bone repair include those cements based on polymethylmethacrylate (PMMA) and those based on calcium phosphate minerals. Although PMMA cements have been used with success, cements based on calcium phosphates, i.e. apatitic cements tend to be more biocompatible and more closely resemble the natural mineral structure of bone. For example, hydroxyapatite is a popular bone substitute material because of its close chemical and/or structural resemblance to natural bone.
Calcium phosphate cements, also known as apatitic cements, generally are produced from an acidic source and a basic source. Currently, apatitic cements are available in either three component or two component forms. In three component apatitic cements, an acidic source is kept separate from a basic source, as well as the third component which is a lubricant, until the cement is to be used, e.g. during a bone repair operation. When the cement is to be used, the user, e.g. a physician or nurse, first mixes the acidic source with the basic source. The user then mixes the combined sources with a lubricant to obtain a moldable paste. The moldable paste is then applied to the bone site, where it sets into a solid, bone-like structure. Although three component cements are advantageous in that they are storage stable and have a long shelf life, the need to perform a two step mixing process has disadvantages. A two step mixing process adds to the complexity of, as well as the time required for, the overall treatment procedure.
In an effort to address the disadvantages found in three component cements, two component apatitic cement compositions have been developed. In these two component cements, the acidic and basic sources are provided to the user premixed as a single dry component. To use the cement, the user combines this dry component with the lubricant in a single mixing step. Although using two component cements requires one step mixing, the cements tend to be less stable than their three component counterparts. Since the acidic and basic sources are not separate in the dry component of the two component cement compositions, a slow reaction between the two sources may occur even though the cement has not been combined with a lubricant. This slow reaction between the two sources adversely affects the stability of the cements and makes storage for extended periods of time difficult.
Thus, there is significant interest in the development of two component apatitic cements which exhibit improved storage stability. Such cements would provide the user with simple mixing regimens. In addition, significant reaction between the acidic and basic sources in the dry component of the cement would not occur before the dry component is combined with the lubricant. Thus, the cements could be stored for extended periods of time prior to use.
Relevant Literature
U.S. Pat. Nos. 4,888,610; 5,053,212; 5,129,905; and 5,178,845 describe various calcium phosphate cement compositions and methods for their production.
TenHuisen, "The Formation of Biocomposites at Physiological Temperature," Masters Thesis, The Pennsylvania State University Graduate School College of Earth and Mineral Sciences, August 1992, describes the formation of an intimate mixture of tetracalcium phosphate and monocalcium phosphate monohydrate by blending in a non-aqueous solvent.
TenHuisen and Brown, Journal of Biomedical Materials Research (1994) 28: 27-33 describe the milling of tetracalcium phosphate with anhydrous dicalcium phosphate.
Lerner et al., Journal of Crystal Growth (1989) 97: 725-730 describe rapid apatite formation from ethanol/water solutions.